Re: [libvirt] [Qemu-devel] [RFC] kvm: x86: export vCPU halted state to sysfs
On Fri, Feb 02, 2018 at 05:23:59PM +0000, Dr. David Alan Gilbert wrote:
* Eduardo Habkost (ehabkost(a)redhat.com) wrote:
> (CCing qemu-devel)
>
> On Fri, Feb 02, 2018 at 09:21:59AM -0500, Luiz Capitulino wrote:
> > On Fri, 2 Feb 2018 14:19:38 +0000
> > Daniel P. Berrangé <berrange(a)redhat.com> wrote:
> > > On Fri, Feb 02, 2018 at 12:15:54PM -0200, Eduardo Habkost wrote:
> [...]
> > > > It would be also interesting to update QEMU QMP documentation to
> > > > clarify the arch-specific semantics of "halted".
> > >
> > > Any also especially clarify the awful performance implications of running
> > > this particular query command. In general I would not expect query-xxx
> > > monitor commands to interrupt all vcpus, so we should clearly warn about
> > > this !
> >
> > Or deprecate it...
>
> We could deprecate the expensive fields on query-cpus, and move
> them to a more expensive query-cpu-state command. I believe most
> users of query-cpus are only interested in qom_path, thread_id,
> and topology info.
Would that data be available without the bql? I ask because if it is
then a small advantage to having a separate command is that the command
could be marked OOB with Peter's new series and never take the lock.
We would need a mechanism to safely walk the CPU list without the
BQL, so I wouldn't bother trying to make a OOB-capable version of
query-cpus unless really necessary.
--
Eduardo